Many Happy Returns will be available via BBC iPlayer from around 2pm on Christmas Eve, report Radio Times.

"A series of seemingly unconnected crimes stretching from Tibet to India to Germany," reads the synopsis. "Sherlock Holmes has been gone for two years. But someone isn't quite convinced that he's dead."

It hasn't yet been confirmed whether Benedict Cumberbatch or Martin Freeman will appear in the episode, which will be available to watch on the BBC's interactive Red Button service.